Ocheyedan and Little Sioux Rivers There are two reports on the geohydrology of the Ocheyedan and Little Sioux River valleys. The Geological Survey Bureau's Open File Report 86-4 is a data report which contains background information on geology (from well logs, bridge borings, and sand and gravel pit descriptions), results of the seismic refraction surveys, drillers' logs for wells drilled for the project, water level data from July 1985 to August 1986, and water quality analyses from extant wells, both municipal and private. The other report, GSB Open File Report 86-3 (Executive Summary), is the main report with extensive text covering availability, aquifer characteristics, and groundwater quality of the aquifer. In addition, there is a field trip guidebook (GSI Guidebook 34) which covers the history and evolution of the Little Sioux River and contains detailed site descriptions.